JP2006135017A - Photoelectric converter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a photoelectric converter with sufficient yield even if film thickness of a semiconductor layer is very thin to be not more than 50 μm in the photoelectric converter, and to provide the photoelectric converter. <P>SOLUTION: The photoelectric converter is provided with the semiconductor layer, a surface electrode formed on the main face of the semiconductor layer, and a back electrode formed on a face confronted with the main face of the semiconductor layer. In the back electrode, a face on a side which is brought into contact with the semiconductor layer is larger than a contact face in the semiconductor layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric conversion device and a manufacturing method thereof, and more specifically to a solar cell and a manufacturing method thereof.

  As a conventional technique, a photoelectric conversion device as shown in FIG. In the photoelectric conversion device according to this prior art, in FIG. 7, a front electrode 102 is formed on the main surface of a semiconductor substrate 101 that receives sunlight, and a back electrode 103 is formed on the opposite main surface. Here, in FIG. 7, (a) is a plan view of the photoelectric conversion device, (b) is a plan view seen from a surface facing (a), and (c) is a cross section of the photoelectric conversion device. FIG.

  However, in the above-described prior art, in the case where an ultra-thin single crystal semiconductor having a semiconductor layer thickness of 50 μm or less is formed on the semiconductor substrate 101, it is difficult to manufacture by the method described in this document.

  Specifically, the photoelectric conversion device manufactured by the conventional technique shown in FIG. 7 is formed so that the area of the back electrode 103 is small with respect to the semiconductor substrate 101 and in particular does not cover the outer periphery of the semiconductor substrate 101. .

  This is because if the back electrode 103 is formed outside the outer periphery of the semiconductor substrate 101, the back electrode 103 may come into contact with the side surface of the semiconductor substrate and a short circuit may occur.

  However, when an ultra-thin single crystal semiconductor with a semiconductor layer thickness of 50 μm or less is used, the mechanical strength of the ultra-thin single crystal semiconductor is low unless the back electrode is formed up to the outer periphery of the semiconductor substrate. Even if a slight impact is applied, cracks and chips are generated, resulting in a decrease in yield.

Therefore, in the conventional method, it is difficult and difficult to produce a single crystal semiconductor solar cell having an extremely thin film thickness of 50 μm or less.
JP 2004-140023 A

  The present invention has been made in order to solve the above-described problems of the prior art, and an object of the present invention is to provide a photoelectric conversion device that is a very thin film having a semiconductor layer thickness of 50 μm or less. It is an object of the present invention to provide a method that can be manufactured with high yield and the photoelectric conversion device.

  According to one aspect of the present invention, a semiconductor layer, a surface electrode formed on the main surface of the semiconductor layer, and a back electrode formed on a surface facing the main surface of the semiconductor layer are provided. A photoelectric conversion device is provided, wherein a surface of the back electrode in contact with the semiconductor layer is larger than a contact surface of the semiconductor layer.

  Preferably, the semiconductor layer is made of a single crystal semiconductor.

  Preferably, the semiconductor layer has a thickness in the range of 2 to 50 μm.

  Preferably, the thickness of the back electrode is in the range of 1-8 μm.

  According to another aspect of the present invention, a step of laminating a semiconductor layer on a substrate, a step of etching the semiconductor layer to form a surface electrode on the main surface of the semiconductor layer, and a step of removing the substrate And a step of forming a back electrode on a surface of the semiconductor layer that faces the surface on which the surface is formed, and a method of manufacturing a photoelectric conversion device that is in contact with the semiconductor layer in the back electrode The surface of is larger than the contact surface in the said semiconductor layer, The manufacturing method of the photoelectric conversion apparatus characterized by the above-mentioned is provided.

  Preferably, before the step of removing the substrate and after the step of forming the surface electrode, etching the semiconductor layer to form a mesa on the substrate; the semiconductor layer, the surface electrode, and the The method further includes forming a resin so as to cover the mesa, forming a support substrate on the resin, and applying pressure to the support substrate in the substrate direction.

  Preferably, after the step of forming the back electrode, the method further includes a step of removing the resin by etching, and also removing the support substrate.

  Preferably, the semiconductor layer is made of a single crystal semiconductor.

  Preferably, the semiconductor layer has a thickness in the range of 2 to 50 μm.

  Preferably, the thickness of the back electrode is in the range of 1-8 μm.

  ADVANTAGE OF THE INVENTION According to this invention, even if the film thickness of a semiconductor layer is a very thin film, the method and the said photoelectric conversion apparatus which can manufacture a photoelectric conversion apparatus with a sufficient yield are provided.

  A photoelectric conversion device of the present invention includes a semiconductor layer, a front surface electrode formed on the main surface of the semiconductor layer, and a back electrode formed on a surface opposite to the main surface of the semiconductor layer. The device is characterized in that a surface of the back electrode in contact with the semiconductor layer is larger than a contact surface of the semiconductor layer.

  According to the method for manufacturing a photoelectric conversion device of the present invention, a step of laminating a semiconductor layer on a substrate, a step of etching the semiconductor layer to form a surface electrode on the main surface of the semiconductor layer, A method of manufacturing a photoelectric conversion device, comprising: removing a substrate; and forming a back electrode on a surface of the semiconductor layer that faces the surface on which the surface is formed. The contact surface is larger than the contact surface in the semiconductor layer.

  As described above, since the contact-side surface of the back electrode is larger than the contact surface of the semiconductor layer, the semiconductor layer can be prevented from being cracked or chipped in the manufacturing process of the photoelectric conversion device, and the manufacturing yield can be improved. it can.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of a photoelectric conversion device of the present invention, in which (a) is a plan view seen from the front electrode side, (b) is a plan view seen from the back electrode side, and (c) is a plan view. It is sectional drawing of a photoelectric return apparatus.

  As shown in FIG. 1, the photoelectric conversion device of the present invention has a surface electrode 3 and a back electrode 4 formed on both main surfaces of a semiconductor layer 2. The front surface electrode 3 is formed on the main surface of the semiconductor layer 2 in a comb shape as shown in FIG. 1A, and the back surface electrode 4 is formed in the semiconductor layer 2 as shown in FIG. The contact surface is in contact with the semiconductor layer 2 including the outside.

  As can be seen from FIGS. 1B and 1C, in the photoelectric conversion device of the present invention, the surface of the back electrode 4 that is in contact with the semiconductor layer 2 is larger than the contact surface of the semiconductor layer 2. It is characterized by. Thereby, even when the semiconductor layer is extremely thin, defects such as cracks and chips can be prevented in the manufacturing process, and the yield can be improved.

  Here, in the present invention, the contact surface in the semiconductor layer is the surface of the main surface of the semiconductor layer 2 that is in contact with the back electrode 4. Further, the surface of the back electrode that is in contact with the semiconductor layer 2 refers to the surface of the main surface of the back electrode 4 that is in contact with the semiconductor layer 2. That is, in the present invention, the surface of the back electrode 4 on the side in contact with the semiconductor layer 2 is larger than the surface of the semiconductor layer 2 in contact therewith.

  Next, the manufacturing method of the photoelectric conversion of this invention is demonstrated using FIGS. 2-6 is schematic sectional drawing which shows each of the manufacturing process of the photoelectric conversion apparatus of this invention. First, as shown in FIG. 2, the semiconductor layer 2 is stacked on the semiconductor substrate 5, and the surface electrode 3 is formed on the main surface of the semiconductor layer 2.

  In the present invention, a semiconductor substrate of a simple element such as Si or Ge can be used as the semiconductor substrate, or a compound semiconductor substrate such as GaAs may be used. The semiconductor substrate is preferably a single crystal semiconductor substrate. This is because by using a single crystal, a semiconductor layer can be easily epitaxially grown on the semiconductor substrate.

  A semiconductor layer including a pn junction is formed on the semiconductor substrate. If necessary, it may be a semiconductor layer composed of a multilayer film including a pn junction. The material of the semiconductor layer that can be used in the present invention is not particularly limited, and a known material can be used depending on the application. For example, Si, Ge, GaAs, InP, InGaP, and InGaAs are used. be able to. Further, the semiconductor layer is preferably an epitaxial layer with a small strain in order to remove all or part of the semiconductor substrate.

  In the present invention, the semiconductor layer can be deposited by epitaxial growth as described above, and as its method, MBE method, MOCVD method, VPE method or the like can be used. The semiconductor layer preferably has a layer thickness of 2 μm or more and 50 μm or less for use as a photoelectric conversion device. If the thickness is less than 2 μm, light absorption is insufficient, which may deteriorate the photoelectric conversion efficiency. If the thickness exceeds 50 μm, the weight of the photoelectric conversion device increases, but the photoelectric conversion efficiency reaches a peak, There is a problem that the photoelectric conversion efficiency is degraded. Preferably, they are 3 micrometers or more and 10 micrometers or less.

  Next, the process of forming the surface electrode on the main surface of the semiconductor layer will be described. Specifically, a surface electrode is formed on the semiconductor layer by, for example, a normal photolithography method, a vapor deposition method, a lift-off method, or a sintering method. In addition, other ordinary electrode forming methods can be used. In the present invention, a material that can be used for the surface electrode is not particularly limited, and those known in the art can be used. For example, a conductive material made of silver (Ag) can be given as an example.

  Here, it is preferable that the surface electrode has a comb shape as shown in FIGS. In the present invention, the present invention is not limited to the comb shape, and any other electrode shape that can function as a photoelectric conversion device can be employed.

  As a method for forming the comb shape or the like, a known method can be used. Specifically, the semiconductor layer is etched into a desired shape through a mask, and a surface electrode is formed in the etched portion. And the like.

  Next, as shown in FIG. 3, a mask 6 is formed in a desired portion on the semiconductor layer 2 and the surface electrode 3 by photolithography, and unnecessary portions are removed by etching, for example, by an etching process. Form.

  In the step of forming the mesa, the etching depth can be appropriately selected according to the purpose. For example, when a part of the semiconductor layer 2 is used for a photoelectric conversion device, it is preferable to etch away to a lower layer part of the layer forming the semiconductor layer, or to etch away at least part of the semiconductor substrate. Further, when the entire semiconductor layer 2 is used in a photoelectric conversion device, it is preferable that the entire semiconductor layer 2 is removed by etching, or at least a part of the semiconductor substrate 5 is removed by etching. Further, in the case where the semiconductor substrate 2 is used in a photoelectric conversion device including a part of the semiconductor substrate 5 in addition to the entire layer of the semiconductor layer 2, it is preferable to etch away to an unnecessary thickness of the semiconductor substrate 5.

  The etching for forming the mesa may be a dry etching method or a wet etching method, but it is preferable to use a selective etching method that substantially stops the progress of etching in a specific layer. Moreover, before performing the process of forming a surface electrode, the process of forming a mesa may be performed previously.

  Next, as shown in FIG. 4, a resin 8 is formed so as to cover the mesa 7, the semiconductor layer 2, and the surface electrode 3. The tree 8 can be formed by spin coating. Moreover, as the material of the resin 8, a material obtained by dissolving a phenol resin in an organic solvent such as isopropyl alcohol or cyclohexane can be used.

  Next, in order to simplify the process after etching of the semiconductor substrate 5, it is preferable to previously form the support substrate 9 on the semiconductor layer 2 by dissolving the resin 8. The support substrate 9 preferably has an appropriate hardness. As described above, the support substrate 9 is bonded to the support substrate 9 through the resin 8 obtained by coating the surface electrode 3, the semiconductor layer 2, and the mesa 7 by spin coating.

  After that, as shown in FIG. 5, a part or all of the semiconductor substrate 5 or a part of the semiconductor layer 2 is removed by etching by a normal etching process.

  Next, after the etching of the semiconductor substrate 5, as shown in FIG. 6, a mask 10 is appropriately formed in an unnecessary portion according to the application by a normal masking method, and the back electrode 4 is formed by a vapor deposition method or the like. For the formation of the back electrode 4, other conventional electrode forming methods known in the art can be used.

  In the formation of the back electrode, since the resin 8 is covered up to the side surface of the mesa 7, no electrode is formed on the side surface of the mesa 7. Therefore, the back electrode 4 does not come into contact with the side surface of the mesa 7, and the characteristics of the photoelectric conversion device due to leakage current and the like are not impaired.

  The back electrode 4 is made of a conductive material made of, for example, silver (Ag). The back electrode 4 is a full surface electrode. In addition, all electrode shapes that can function as a photoelectric conversion device can be employed. However, it is necessary to make it larger than the contact surface of the semiconductor layer 2.

  In the present invention, the thickness of the back electrode 4 is preferably 1 μm or more and 8 μm or less. This is because a film thickness of 1 μm or more is required for the back electrode 4 to function as a support for the semiconductor layer 2. If the film thickness of the back electrode exceeds 8 μm, the semiconductor layer 2 may be bent due to the difference in the coefficient of thermal expansion between the semiconductor layer 2 and the back electrode 4. More preferably, they are 2 micrometers or more and 5 micrometers or less.

  Thereafter, by removing the resin 8 by etching, the support substrate 9 is also removed. The mask 10 is also removed by etching or the like. In this way, the photoelectric conversion device of the present invention as shown in FIG. 1 can be manufactured.

  In the present invention, a step of further forming an antireflection film on the surface electrode 3 may be provided. Furthermore, you may provide the process of connecting the interconnector for obtaining an electrical connection outside.

  A photoelectric conversion device in which a back electrode is formed at least including the outer side of the outer peripheral side surface of the main surface that receives sunlight without the back electrode being in contact with the side surface of the mesa by the method for manufacturing a photoelectric conversion device of the present invention described above. Can be produced.

  In the photoelectric conversion device of the present invention, since the back electrode is formed including at least the outer peripheral side surface portion that receives sunlight, there is no portion where the single crystal semiconductor of the ultrathin film exists alone, and thus mechanically The strength is increased and the semiconductor layer is not cracked or chipped by an impact or the like, so that the cost and weight of the photoelectric conversion device can be reduced.

  In Examples, a photoelectric conversion device as shown in FIG. 1 was produced. First, as shown in FIG. 2, the multilayer semiconductor layer 2 was epitaxially grown on the semiconductor substrate 5 using a Ge material by a metal organic chemical vapor deposition (MOCVD) method. Here, the multilayer semiconductor layer 2 is a p-type GaAs layer having a thickness of 1 μm and an n-type GaAs layer having a thickness of 3 μm. When making a photoelectric conversion apparatus function as a solar cell, the semiconductor layer 2 should just be a total film thickness of 2 micrometers or more. Next, a surface electrode 3 mainly composed of silver (Ag) was formed on the main surface of the multilayer semiconductor layer 2 by combining a conventionally known photolithography method, vapor deposition step method, lift-off method, and heat treatment.

  Next, as shown in FIG. 3, an etching mask 6 is formed in a necessary portion on the main surface of the multilayer semiconductor layer 2 by a conventionally known photolithography process, and the unnecessary multilayer semiconductor layer 2 is wetted. The mesa 7 was formed by etching away using an etching method. As the etching solution, a mixed aqueous solution of citric acid and hydrogen peroxide was used.

  Next, as shown in FIG. 4, the surface electrode 3 and the mesa 7 are coated on the multilayer semiconductor layer 2 on which the mesa 7 is formed by spin coating with a phenol resin 8 dissolved in an organic solvent such as isopropyl alcohol or cyclohexane. The resin 8 was formed by lightly volatilizing the solvent at 100 ° C. in an oven. Further, the glass support substrate 9 is placed on the resin 8 and heated at 140 ° C., and the Ge substrate 5 including the multilayer semiconductor 2 and the glass support substrate 9 are interposed via the resin 8 by applying pressure uniformly over the glass. Integrated.

Next, as shown in FIG. 5, the Ge substrate 5 integrated with the glass support substrate 9 is immersed in a mixed aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H ₂ O ₂ ) to thereby form the Ge substrate 5. Was removed by etching.

  Next, as shown in FIG. 6, a mask 10 is formed in an unnecessary portion on the surface opposite to the main surface of the multilayer semiconductor layer 2 by a conventionally known masking process, and silver (Ag) is mainly formed by vapor deposition. A back electrode 4 as a material was formed on the opposite surface of the main surface of the multilayer semiconductor layer 2. The film thickness of the back electrode 4 was set to 8 μm or less, which is a film thickness of 1 μm or more necessary for the function using the back electrode 4 as a support for the semiconductor layer 2 and the curvature of the semiconductor layer 2 is small.

  At this time, since the resin 8 is present on the side surface of the mesa 7, the back electrode 4 is not formed on the side surface of the mesa and can be formed including the outer side of the outer peripheral side surface of the main surface that receives sunlight. . Further, the surface obtained by mesa formation and the surface obtained by substrate etching must be matched. In this embodiment, the citric acid-based etching solution can substantially etch only the GaAs layer, and the hydrofluoric acid-based etching solution can substantially etch only Ge. In this embodiment, the combination of the semiconductor material and the etchant is used. However, other semiconductor materials and etchants can be used by selecting a combination of the etchant and the semiconductor material that can be etched substantially selectively. is there.

  Thereafter, although not shown, the mask 10 and the metal film deposited on the mask 10 are removed by a lift-off method. Thereafter, the resin 8 is dissolved by dipping in acetone, the glass support substrate 9 is removed, and the photoelectric conversion device shown in FIG. 1 is obtained through a conventionally known organic cleaning process. This photoelectric conversion device can be used for, for example, a space solar cell (for artificial satellite mounting).

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic diagram of the photoelectric conversion apparatus of this invention. It is a schematic sectional drawing of the manufacturing process of the photoelectric conversion apparatus of this invention. It is a schematic sectional drawing of the manufacturing process of the photoelectric conversion apparatus of this invention. It is a schematic sectional drawing of the manufacturing process of the photoelectric conversion apparatus of this invention. It is a schematic sectional drawing of the manufacturing process of the photoelectric conversion apparatus of this invention. It is a schematic sectional drawing of the manufacturing process of the photoelectric conversion apparatus of this invention. It is a schematic diagram of the conventional photoelectric conversion apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Photoelectric conversion device, 2,101 Semiconductor layer, 3,102 Front electrode, 4,103 Back electrode, 5 Semiconductor substrate, 6,10 Mask, 7 mesa, 8 Resin, 9 Support substrate.

Claims (10)

A photoelectric conversion device comprising: a semiconductor layer; a surface electrode formed on a main surface of the semiconductor layer; and a back electrode formed on a surface facing the main surface of the semiconductor layer,
The photoelectric conversion device according to claim 1, wherein a surface of the back electrode in contact with the semiconductor layer is larger than a contact surface of the semiconductor layer.   The photoelectric conversion device according to claim 1, wherein the semiconductor layer is made of a single crystal semiconductor.   The photoelectric conversion device according to claim 1, wherein a thickness of the semiconductor layer is in a range of 2 to 50 μm.   The photoelectric conversion device according to claim 1, wherein a thickness of the back electrode is in a range of 1 to 8 μm.   Laminating a semiconductor layer on a substrate, etching the semiconductor layer to form a surface electrode on a main surface of the semiconductor layer, removing the substrate, and forming the surface in the semiconductor layer Forming a back electrode on a surface opposite to the processed surface, and a method of manufacturing a photoelectric conversion device, wherein a surface of the back electrode in contact with the semiconductor layer is a contact surface in the semiconductor layer A method of manufacturing a photoelectric conversion device, wherein the photoelectric conversion device is larger.   Before the step of removing the substrate and after the step of forming the surface electrode, etching the semiconductor layer to form a mesa on the substrate; covering the semiconductor layer, the surface electrode, and the mesa The method of claim 5, further comprising: forming a resin, forming a support substrate on the resin, and applying a pressure to the support substrate in the substrate direction. The manufacturing method of the photoelectric conversion apparatus of description.   The method for manufacturing a photoelectric conversion device according to claim 6, further comprising a step of etching and removing the resin after the step of forming the back electrode, and also removing the support substrate.   The method for manufacturing a photoelectric conversion device according to claim 5, wherein the semiconductor layer is made of a single crystal semiconductor.   The method for manufacturing a photoelectric conversion device according to claim 5, wherein a thickness of the semiconductor layer is in a range of 2 to 50 μm.   10. The method for manufacturing a photoelectric conversion device according to claim 5, wherein a thickness of the back electrode is in a range of 1 to 8 μm.

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